Danfoss 120Z0372 Surface Sump Crankcase Heater – 80 W / 230 V, with Bottom Insulation | For SY-SZ 240-380

Danfoss 120Z0372 is a surface sump heater bonded externally to the compressor sump base. When the compressor stops, refrigerant migrates to the sump, the coldest point of the circuit, and condenses in the oil; the heater prevents this migration by keeping the sump base at a temperature above that of the oil. The product comes with a bottom insulation pad — it prevents heat from escaping downward and increases efficiency.

Surface Type Heater Bonded to the Sump Base

Compared with the belt type, the surface type heater heats the underside of the oil sump directly; it fits the low, wide sump base of scroll compressors better and is preferred in installations where wrapping a belt around the shell is difficult. In a system without a crankcase heater, or with a faulty one, the oil is diluted by refrigerant; at the first start the oil film breaks, bearing and piston wear begins, and in severe cases liquid slugging destroys the compressor completely. A crankcase heater is considered mandatory in all units installed outdoors and with long standstill periods; it is also a condition required by compressor warranties.

Technical Specifications (Official Danfoss Catalog)

• Brand / Code: Danfoss 120Z0372 (genuine spare part)
• Type: Surface sump heater + bottom insulation included
• Power: 80 W | Voltage: 230 V
• Certificates: CE + UL
• Compatible Compressors: Danfoss SY 240 / SY 300 / SY 380, SZ 240 / SZ 300 / SZ 380
• Other voltages for the same body: 400 V → 120Z0373 · 575 V → 120Z0375
• Smaller body equivalent: 56 W for SM/SZ 175-185 and SH 180-485 → 120Z0376 (230 V)

• 🔧 Clean the sump base before bonding: Oil, rust and paint residue impair heat transfer; the heater can overheat itself and burn out.
• Do not skip the insulation pad — the bottom insulation prevents heat from escaping to the surroundings and noticeably increases heater effectiveness.
• Commissioning: After a long standstill, it is recommended that the heater be energized for at least 8-12 hours before starting the compressor. It is wired so that it is energized when the compressor is stopped and de-energized when it is running (via the contactor auxiliary contact).
• Check: A sound 80 W / 230 V heater has a resistance of approximately 660 Ω; if the measurement shows an open circuit, the heater has burned out.